مقال علمي، لمن أراد معلومات فيزيائية حول الموضوع criterion of progressive collapse
خاصية الانهيار المتتالي (إن ترجمت بدقة)
والمقال صادر عن نقابة المهندسين المدنيين لأمريكا الشمالية:

http://www.civil.northwestern.edu/people/b.../Papers/466.pdf

وهو يجري محاكاة حاسوبية بعد نمذجة رياضية للطاقة الحركية للطائرة التي لا تكفي لانهيار المبنى ولكن مع الحرارة المتولدة من الاحتراق وانهيار الطابق كاملاً تثبت الدراسة حتمية انهيار المبنى طابقاً بعد طابق كما تتفتت قطعة تراب تحت المطر...

ويكفي معرفة أن صرخة بقرب جبل قد تؤدي إلى انهيار ثلجي ذي طاقة هائلة، وكم طاقة هذه الصرخة ؟

( سؤال على الهامش : هل حاولتم أن تثنوا شمعة لم تذب بعد لنعرف أن بالإمكان إفقادها مقاومتها الميكانيكية قبل ذوبانها أي بدرجة حرارة تقل بكثير عن درجة الانصهار...
كذلك كل المواد الأخرى (انظروا البند الثاني من مراحل الانهيار في المقالة.... )

أنسخ الجزء المهم من المقالة لمن لم يرد قراءة كل شيئ، وهو عن مراحل الانهيار وأسباب كل مرحلة :

1. About 60% of the 60 columns of the impacted face of framed
tube
and about 13% of the total of 287 columns were severed,
and many more were significantly deflected. This
caused stress redistribution, which significantly increased the
load of some columns, attaining or nearing the load capacity
for some of them.
2. Because a significant amount of steel insulation was stripped,
many structural steel members heated up to 600°C, as confirmed
by annealing studies of steel debris
NIST 2005 the
structural steel used loses about 20% of its yield strength
already at 300°C, and about 85% at 600°C
NIST 2005;
and exhibits significant viscoplasticity, or creep, above
450°C
e.g., Cottrell 1964, p. 299, especially in the columns
overstressed due to load redistribution; the press reports right
after September 11, 2001 indicating temperature in excess of
800°C, turned out to be groundless, but Bažant and Zhou’s
analysis did not depend on that.
3. Differential thermal expansion, combined with heat-induced
viscoplastic deformation, caused the floor trusses to sag. The
catenary action of the sagging trusses pulled many perimeter
columns inward
by about 1 m, NIST 2005. The bowing of
these columns served as a huge imperfection inducing multistory
out-of-plane buckling of framed tube wall. The lateral
deflections of some columns due to aircraft impact, the differential
thermal expansion, and overstress due to load redistribution
also diminished buckling strength.
4. The combination of seven effects—
1 Overstress of some
columns due to initial load redistribution;
2 overheating
due to loss of steel insulation;
3 drastic lowering of yield
limit and creep threshold by heat;
4 lateral deflections of
many columns due to thermal strains and sagging floor
trusses;
5 weakened lateral support due to reduced in-plane
stiffness of sagging floors;
6 multistory bowing of some
columns
for which the critical load is an order of magnitude
less than it is for one-story buckling; and
7 local plastic
buckling of heated column webs—finally led to buckling of
columns Fig. 1
b. As a result, the upper part of the tower
fell, with little resistance, through at least one floor height,
impacting the lower part of the tower. This triggered progressive
collapse because the kinetic energy of the falling upper
part exceeded
by an order of magnitude the energy that
could be absorbed by limited plastic deformations and fracturing
in the lower part of the tower.

(f)